1. Field of the Invention
The present invention relates to a communication system in which a wire communication network is linked with another wire communication network or radio devices via radio waves.
2. Related Art
It is proposed that a vehicle controls itself for safety based on information gathered from various sensors disposed therein and/or radars disposed thereon for detecting obstacles around the vehicle. However, the radar for detecting obstacles in front can detect only the preceding vehicle, that is, it cannot detect vehicles running before the preceding vehicle. Therefore a driver should see the vehicles in front with his/her own eyes for preventing his/her vehicle from being involved in a road traffic accident such as a pileup. That is, the control based on the information from the radar does not effectively prevent the vehicle from being involved in the traffic accident.
It is further proposed that a driver in a moving vehicle obtains information on a traffic jam or the like utilizing vehicle-road communication which is performed between on-board equipment (OBE) installed on the vehicle and road-side units (RSUs) provided in the vicinity of roads. However, the vehicle sometimes runs out of the communication area or within an area in which communication with the RSU is temporarily impossible. Such an area is formed by, for example, other vehicles that shadow the vehicle. When the vehicle is stuck in traffic, it may stay out of the communication area for a relatively long time. Accordingly, the vehicle is not always able to communicate with the RSU, and therefore the driver is not necessarily able to obtain the information timely.
Then it is proposed that vehicle-vehicle communication, which is performed between the vehicles, is utilized in order to overcome the above problems. If the vehicle-vehicle communication is possible, the vehicle can obtain the information from other vehicles. Then the vehicle can control itself based on the obtained information so as to prevent itself from being involved in a traffic accident. Further a vehicle, which has obtained the information from the RSU by the vehicle-road communication, may relay the obtained information to another vehicle. Thus the vehicle, which cannot communicate with the RSU, can indirectly obtain the information provided by the RSU.
Further, it is proposed that devices, which are installed in or brought into the vehicle, are interconnected so that an in-vehicle LAN is established. The devices belonging to the in-vehicle LAN include vehicle-road communication equipment, vehicle-vehicle communication equipment, vehicle navigation equipment, a portable information device, ECUs and the like. If the in-vehicle LAN is thus established, the devices belonging to the in-vehicle LAN can share various information and consequently the vehicle can control itself with more sophistication.
Further, the devices belonging to the in-vehicle LAN can exchange the various information with devices belonging to another in-vehicle LAN established in another vehicle by the vehicle-vehicle communication via the vehicle-vehicle communication equipment. As a result, the driver or an occupant can obtain highly developed information.
However, the frame format or signal format of a signal transmitted via wires are usually different from that of a signal transmitted via radio waves. Therefore the vehicle-vehicle communication equipment connected to the in-vehicle LAN should translate the format of a received signal into the format employed by the in-vehicle LAN, and the format of a signal to be transmitted into the format for radio communication. The communication equipment capable of such translation is complex and expensive.